Add leading 0 in sed substitution

Question

I have input data:

foo 24
foobar 5 bar
bar foo 125

and I\'d like to have output:

foo 024
foobar 005 bar
bar foo 125
         


        

Answer 1

I find the following sed approach to pad an integer number with zeroes to 5 (n) digits quite straighforward:

sed -e "s/\<\([0-9]\{1,4\}\)\>/0000\1/; s/\<0*\([0-9]\{5\}\)\>/\1/"

1. If there is at least one, at most 4 (n-1) digits, add 4 (n-1) zeroes in front
2. If there is any number of zeroes followed by 5 (n) digits after the first transformation, keep just these last 5 (n) digits

When there happen to be more than 5 (n) digits, this approach behaves the usual way -- nothing is padded or trimmed.

Input:

0
1
12
123
1234
12345
123456
1234567

Output:

00000
00001
00012
00123
01234
12345
123456
1234567